This study aims to determine the relative efficacy, tolerability, and safety of the selective serotonin reuptake inhibitor (SSRI) citalopram in the treatment of pediatric functional recurrent abdominal pain (RAP). RAP is common, typically presents in medical settings, and is associated with suffering, impairment, excess service use, and high rates of inadequately treated comorbid anxiety and depressive disorders. No single treatment has been conclusively demonstrated to be efficacious, and the relationship between RAP and comorbid anxiety and depression is poorly understood. A recently completed open trial suggests that citalopram is a promising treatment for RAP and comorbid anxiety and depression. Over a four year period, 100 children and adolescents with RAP between the ages of 7 and 18 years, inclusive, will be recruited by clinical referral and office screening, randomly assigned to citalopram or placebo for 8 weeks of double blind treatment, then returned to the care of the referring physician. Initial citalopram dose will be 10 mg/day, increasing to 20 mg/day after one week, and to 40 mg/day at week four if response is suboptimal and there are no significant side effects. Primary outcomes will be global improvement assessed by the Clinical Global Impression Scale-Improvement (CGI-I) and abdominal pain assessed with the Abdominal Pain Index (API), a well-validated measure of abdominal pain frequency, duration, and intensity. Comorbid psychopathology will be assessed using current state of the art measures and the potential role of anxiety and depression as mediators of treatment response will be secondarily examined, as well as the durability and tolerability of citalopram treatment following completion of the double-blind phase. Citalopram treatment of RAP offers advantages of relative simplicity, economy of scale, and acceptability within the medical setting, as well as the potential to treat both RAP and comorbid anxiety and depressive disorders regardless of the specific attributions of patients, family members, or professionals. Limited exclusion criteria and the delivery of study assessments and interventions within routine practice settings provide for considerably greater external validity than the typical efficacy study, with the potential to inform future studies of treatment effectiveness and dissemination.